This invention relates to orthopedic surgery, more particularly to a prosthetic intervertebral disc replacement system which can be implanted into a suitably prepared intervertebral disc space via minimally invasive surgical techniques to provide for and restore substantial functional normalcy.
The normal intervertebral disc is in essence a complex joint which allows for various articular motions between adjacent vertebral segments. These articular motions, in turn, account for the flexibility and functional mobility of the normal human spine. In the course of a day, the normal intervertebral disc encounters a variety of compressional, rotations and associated flexion or extension movements. In these day to day activities, movements in varying and repetitive combinations accumulate and contribute to the deterioration of natural discs that occurs over time. As with other joints in the human body that deteriorate over time, it would be desirable to have disc replacement prostheses which could be inserted in place of a failed or worn normal disc when it is determined the disc is irreparably damaged and that preservation of functional mobility is required. The time honored method of addressing debilitating symptoms and signs of a degenerative disc is to remove the disc and fuse the two adjacent vertebral bones together. Fusion eliminates motion at the abnormal segment, and while useful at improving debilitating symptoms, the consequence of eliminating natural motions at a single segment is that greater degrees of stress occur above or below that segment. This in turn accelerates degeneration of neighboring intervertebral discs, often necessitating additional fusion surgeries. It would be desirable, therefore, to preserve motion at every disc space and thus retain natural motion and eliminate the adjacent level degeneration that discectomy and fusion seems to produce. Toward this end, an intervertebral disc replacement prosthesis ought ideally to restore and preserve disc space height while permitting sufficient natural motion (flexion, extension, rotation and lateral bending) to prevent excessive stresses on spinal segments above and below the prosthesis.
Several intervertebral disc replacement prostheses are now in production, but none has the capacity to be implanted posteriorly through traditional exposures of the spine, or through smaller incisions, known collectively as minimally invasive surgical techniques.